Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$202.38	11.787%	$226.2345	$226.23	$226.25	$226.20
Purchase #2	$126.57	12.166%	$141.9685	$141.97	$141.95	$142.00
Purchase #3	$117.87	4.509%	$123.1848	$123.18	$123.20	$123.20
Purchase #4	$160.53	3.391%	$165.9736	$165.97	$165.95	$166.00
Purchase #5	$61.62	6.224%	$65.4552	$65.46	$65.45	$65.50
Purchase #6	$34.83	10.608%	$38.5248	$38.52	$38.50	$38.50
Purchase #7	$115.90	13.514%	$131.5627	$131.56	$131.55	$131.60
7 purchase totals =	$819.70		$892.9041	$892.89	$892.85	$893.00